1. Field of the Invention
The present invention relates to a mobile communication system,mobile communication methods, a wireless base station, a mobile station, and programs.
2. Related Background Art
Studies have currently been in progress for applying IP (Internet Protocol), which is a network control protocol prevailing in the Internet, to mobile communication systems in view of seamless connections to the Internet in order to achieve multimedia properties in the mobile communication systems and lower the cost of backbone networks. FIG. 5 shows a configurational example of a wireless base station 10 and a mobile station 20 (collectively referring to mobile stations 20A, 20B) in such a mobile communication system 1. As shown in FIG. 5, the wireless base station 10 includes a transmitter/receiver 11, a wireless link layer processor 12, an IP layer processor 13, an AAL (ATM Adaptation Layer) processor 14, and an ATM (Asynchronous Transfer Mode) transmitter/receiver 15. On the other hand, each mobile station 20 includes a transmitter/receiver 21, a wireless link layer processor 22, and an IP layer processor 23.
In the mobile station 20, user data such as visual, audio, and text data are processed by various applications located in an upper layer and then are fed as a data packet into the IP layer processor 23. The IP layer processor 23 carries out the network control defined by the third layer of the OSI (Open Systems Interconnection) reference model, in which IP is widely used as a protocol. Specifically, the IP layer processor 23 adds the IP address of a mobile station (or a computer on the Internet or the like) to communicate with and its own IP address to a packet from an upper layer, so as to newly assemble an IP packet, and sends thus obtained new IP packet to the wireless link layer processor 22. On the network side, a transmission route of the IP packet is selected according to these IP addresses, and the IP packet is sent to the receiving side.
Subsequently, the wireless link layer processor 22 carries out the link control defined by the second layer of the OSI reference model. Specifically, schedule management for transmitting/receiving IP packets, management for assigning wireless resources such as communication bandwidth to each mobile station 20, and other kinds of control specific to mobile communications such as hand-over are carried out between the wireless link layer processor 22 and the wireless link layer processor 12 of the wireless base station 10. To this aim, various kinds of control information are added to the IP packet from the IP layer processor 23, or a layer 2 packet consisting of control information alone is newly assembled, and thus obtained IP packet is sent to the transmitter/receiver 21. The transmitter/receiver 21 is an apparatus for carrying out the control of the first layer of the OSI reference model, and transmits/receives layer 2 packets in wireless areas in synchronization with the transmitter/receiver 11 of the wireless base station 10. IP packets from the wireless base station 10 are successively sent to the transmitter/receiver 21, wireless link layer processor 22, and IP layer processor 23 in the order reverse of that explained above, so as to be restored to visual, audio, and text data and the like in upper layers.
On the other hand, the wireless base station 10 is characterized in that it has a function of carrying out network control such as IP packet transfer according to the IP addresses mentioned above, i.e., so-called router function. In the wireless base station 10, the transmitter/receiver 11 restores a layer 2 packet from radio signals from the mobile station 20, and sends thus restored packet to the wireless link layer processor 12. As mentioned above, this wireless link layer processor 12 carries out link control in synchronization with the wireless link layer processor 22 of the mobile station 20, so as to restore an IP packet from the layer 2 packet, and sends thus restored packet to the IP layer processor 13. The IP layer processor 13 refers to the destination address added to the IP packet and sends the IP packet, by way of the AAL processor 14 and ATM transmitter/receiver 15, to another wireless base station 10 or a backbone network to which Internet networks or networks of other communication providers are connected. The AAL processor 14 is an apparatus for carrying out the control of the second layer of the OSI reference model, whereas the ATM transmitter/receiver 15 is an apparatus for carrying out the control of the first layer of the OSI reference model.
Meanwhile, LAN (Local Area Network) using radio waves unlike the above-mentioned mobile communication system 1 has currently been coming into wide use. FIG. 6 shows a configurational example of such a wireless LAN system 2. A wireless base station 30 is constituted by a transmitter/receiver 31, a bridge 32, and an Ethernet transmitter/receiver 33, among which the bridge 32 includes a wireless LAN MAC (Media Access Control) layer processor 32A, relay 32B, an address table 32C, and an Ethernet MAC layer processor 32D. On the other hand, a mobile station 40 includes a transmitter/receiver 41 and a wireless LAN MAC layer processor 42, and is connected to a computer 50. The wireless LAN system 2 differs from the above-mentioned communication system 1 in that no apparatus for carrying out the processing defined by the third layer of the OSI reference model exists, whereby the IP layer is not terminated. Namely, IP packets are processed transparently in the wireless LAN system 2.
The computer 50 processes images, data, and the like, so as to generate an IP packet, and sends thus generated packet to the mobile station 40. In the mobile station 40, the wireless LAN MAC layer processor 42 adds two MAC addresses indicating a destination and a sender, and other kinds of control information to the IP packet, thereby generating a layer 2 packet. These MAC addresses are addresses for specifying the wireless MAC layer processor 42 in order to carry out the control defined by the second layer of the OSI reference model, and differ from the above-mentioned IP addresses used for the processing of the third layer. In synchronization with the wireless LAN MAC layer processor 32A on the wireless base station 30 side, the wireless LAN MAC layer processor 42 carries out schedule management for transmitting/receiving IP packets, management for assigning wireless resources such as communication bandwidth to each mobile station 40, and other kinds of control.
The layer 2 packet generated by the wireless LAN MAC layer processor 42 is transmitted as a radio signal to the wireless base station 30 by way of the transmitter/receiver 41. The transmitter/receiver 31 of the wireless base station 30 restores the layer 2 packet from the radio signal, and sends thus restored packet to the bridge 32. The wireless LAN MAC layer processor 32A and Ethernet MAC layer processor 32D within the bridge 32 convert their protocols to each other by way of the repeater 32B, thereby transmitting/receiving layer 2 packets. Here, however, the repeater 32B carries out control for discarding layer 2 packets sent from both processors 32A, 32D, i.e., filtering, according to the information of MAC addresses stored in the address table 32C. For carrying out this processing, the repeater 32B always stores into the address table 32C the value of sender's MAC address added to each layer 2 packet together with information indicative of whether the packet comes from the wireless side or backbone LAN side. When the next layer 2 packet arrives, the repeater 32B refers to the address table 32C. If the MAC address indicative of the destination of this packet is stored in the address table 32C, it can be seen whether the address is located on the wireless side or the backbone LAN side.
For preventing unnecessary transmission of packets from occurring, the repeater 32B sends back packets from the wireless side if their destination is located on the wireless side, so as not to send them to the backbone LAN side. When the destination of packets from the backbone LAN side is located on the backbone LAN side, they are discarded. When the sender and destination of a packet are located on sides opposite from each other, the repeater 32B allows the layer 2 packet to pass therethrough. When the corresponding MAC address is not stored in the address table 32C, the repeater allows the layer 2 packet to pass therethrough, and sends it back to the wireless side if it comes from the wireless side. Thereafter, the layer 2 packet fed into the Ethernet MAC layer processor 32D is sent to the backbone LAN by way of the Ethernet transmitter/receiver 33. Known as an example of standards for such a wireless LAN is IEEE 802.11 defined by IEEE (Institute of Electrical and Electronic Engineers) Also, Ethernet is a standard known as IEEE 802.3.